The boring machine of this invention is intended primarily for use in high production operations where it is necessary to machine an internal spherical surface in a workpiece to a relatively close tolerance dimension and to maintain this dimension within a small tolerance range throughout an extended production period. An automobile differential gear housing is an example of a workpiece having an internal spherical surface that can be formed by the tool of this invention.
In a typical machining operation for this type of workpiece, the latter are moved progressively through a work station of the machine, and as each workpiece enters the station it is suitably located and clamped in position for the boring operation. The boring bar is then advanced to bring the cutting element into position to make the cut, and the cutting element is swung in an arcuate path while revolving bodily about the rotational axis of the boring bar. Thereafter, the boring bar is retracted to clear the workpiece and the latter is removed while a new workpiece is being moved into the work station. This completes the operating cycle of the machine.
It is conventional practice to check the radius dimension of workpieces coming from the work station either manually or by suitable automatic means such as the apparatus disclosed in the Chynoweth U.S. Pat. No. 3,914,678 dated Oct. 21, 1975 and owned by the assignee of the present application. When the radius dimension approaches either the minimum or the maximum permissible tolerance limit, the cutting element is reset to a larger or smaller radius that will make the cut more nearly midway of the tolerance range specified. These radial adjustments are made periodically as required by tool wear or tool build-up usually in increments of one half thousandths inches when the machining is to a close tolerance dimension.
Heretofore, it has been the practice to adjust the cutting element at the end of an operating cycle. This can be done either manually or automatically by known means but all such means have required that the entire rotary drive for the boring bar be stopped before the adjustment can be made. The time spent in stopping rotation of the boring bar, in making the necessary adjustment, and in getting the drive back to operational speed represents lost production time. In practice, adjustments must be made sufficiently often so that they interrupt the normal cycle of the machine and result in a significant production loss.
The purpose of the present invention is to provide a machine of the type hereinabove described in which the cutting element can be adjusted precisely radially to a predetermined dimension, or to compensate for either tool wear or tool build-up, automatically while the boring bar is being rotatably driven, whereby there is no interruption or delay in the operating cycle of the machine and consequently no loss in production of parts produced by the machine as a result of making the adjustment.